<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>正方形动画</title>
    <link rel="stylesheet" href="css/index.css">
</head>
<body>
    <div class="boss">
        <div class="common front" title="front"></div>
        <div class="common later" title="later"></div>
        <div class="common top" title="top"></div>
        <div class="common bottom" title="bottom"></div>
        <div class="common left" title="left"></div>
        <div class="common right" title="right"></div>
    </div>
</body>
</html>